Hie guys .Help please .I am trying to design a closed loop feed braking system to control the brakes using a PLC for a locomotive (10 gauge). I was planning on using a Hall Effect sensor to pick up rotational speed and also measure it, I have just been told it will not be as accurate. Some suggested I try a tachogenerator and another suggested to me to convert a PWM output into a voltage output but I don’t know where to start. Thanks you?
A PLC have an input port for optical encoder. I suggest you to use an optical encoder.
And, the resolution of the encoder is depended on rotational speed of your system.
I don't know much about tachometer or Hall effect sensors. But, for PWM, it is best to use DAC output so you have shorter sampling intervals.
Ben, I don't understand your question very well. I gather that you have a rotating drive shaft that presumably connects a drive motor to one or more wheels. Are you trying to control a regenerative braking system by switching the resistance in the braking circuit? Are you trying to detect wheel slip? What determines how much braking you need? What is your requirement for "accuracy"? How were you planning to use the Hall Effect Sensor--to measure the braking current? Hall sensors are typically used to measure DC current and can be fairly accurate, but if you are just dissipating power in a resistor bank you can do the same thing quite cheaply by just measuring the voltage across the load resistors. This solution would not give you any information about the rotational speed of the shaft or wheel slip, however. If you need to measure the speed of he shaft/wheel, then the suggestion above about encoders is valid, although you may be able to build a more robust system by using an inductive proximity sensor to sense a keyway on the shaft or the teeth of a gear or sprocket. Inductive sensors are typically impervious to water, dirt, grease, etc. and also much less fragile if mechanical shock is an issue than an optical encoder would be. And many PLCs do have inputs specifically for pulse inputs from speed sensors.
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